Certain articles, such as rubber vehicle tires and synthetic-resin scraps, can be embrittled by deep cooling with a circulated cooling gas so that their subsequent low-temperature milling can be effected with ease. The above-mentioned copending applications described various systems for carrying out the low-temperature embrittlement and low-temperature milling of various articles and materials using these principles. It is also known to deep-cool articles by heat exchange with a circulated cooling gas, e.g. nitrogen, as, for example, is the case with the cooling of electrical components such as magnets in superconductive or cryogenic systems.
One of the most effective ways of lowering the temperature of the closed-cycle recirculated cooling gas is the injection of a coolant, usually of the same composition as the cooling gas, in liquid form into the circulation system.
Thus, it is already known, in cold-milling processes or in the cooling of objects or materials of various kinds, to abstract heat from the articles or materials with a circulated cooling gas and, after this gas has been heated in heat exchange with the objects, to mix with it a deep-cooled liquid coolant to cool down the recirculated gas and thus contribute cold to the system corresponding to the heat abstracted and maintain a predetermined cooling-gas temperature at which it is contacted with the articles.
The liquefied cooling medium (coolant) is injected by nozzles into the circulating path of the cooling gas at higher pressure than the latter and in a boiling state. As a result of the injection of the coolant into the cooling-gas recirculation path and the pressure differential to which the injected medium is subjected at the nozzle, a portion of the injected cooling medium expands, causing a condensation thereof and the formation of droplets which are entrained with the cooling gas over relatively long distances of, for example, 4 to 6 meters, until these droplets evaporate by heat exchange and temperature equilibration within the cooling-gas stream into which they are introduced.
Depending upon the pressure differential and the temperatures of the injected coolant and the cooling-gas into which it is injected, therefore, the complete expansion and complete heat exchange of the injected medium with the cooling gas may not be complete until the mixture has traveled from the injection site to the aforementioned significant distance therefrom.
In most cases, such long equilibration stretches are not tolerable and hence existing systems have had the problem that droplets of incompletely evaporated liquid coolant contacted the objects, articles or components which were to be cooled, thereby producing local supercooling, spontaneous fragmentation or breakage of the articles, materials or objects, or irregular cooling thereof.
It has been proposed to eliminate the problem by providing ahead of the injection site, along the path of the coolant to be injected, a nozzle which regulates the supply of the liquefied coolant into the circulating path of the cooling gas. This is intended to bring about a preliminary expansion with gas formation of the coolant to be injected before it is actually introduced into the recirculated cooling gas.
A disadvantage of this system is that, instead of relatively small flow rates of the added liquid, relatively large (by volume) quantities of gas must be introduced into the recirculating cooling gas by the nozzles. As a practical matter it is found that the injection of gas into the recirculating stream is seldom uniform so that significant temperature fluctuations are produced in the cooling gas and control of the temperature thereof is difficult or impossible.